Imports System
Imports System.Collections.Concurrent
Imports System.Threading
Imports System.Threading.Tasks
Module ObjectPoolExample
Public Class ObjectPool(Of T)
Private _objects As ConcurrentBag(Of T)
Private _objectGenerator As Func(Of T)
Public Sub New(ByVal objectGenerator As Func(Of T))
If objectGenerator Is Nothing Then Throw New ArgumentNullException("objectGenerator")
_objects = New ConcurrentBag(Of T)()
_objectGenerator = objectGenerator
End Sub
Public Function GetObject() As T
Dim item As T
If _objects.TryTake(item) Then Return item
Return _objectGenerator()
End Function
Public Sub PutObject(ByVal item As T)
_objects.Add(item)
End Sub
End Class
Sub Main()
Dim cts As CancellationTokenSource = New CancellationTokenSource()
' Create an opportunity for the user to cancel.
Task.Run(Sub()
If Console.ReadKey().KeyChar = "c"c Or Console.ReadKey().KeyChar = "C"c Then
cts.Cancel()
End If
End Sub)
Dim pool As ObjectPool(Of TestClass) = New ObjectPool(Of TestClass)(Function() New TestClass())
' Create a high demand for TestClass objects.
Parallel.For(0, 1000000, Sub(i, loopState)
Dim mc As TestClass = pool.GetObject()
Console.CursorLeft = 0
' This is the bottleneck in our application. All threads in this loop
' must serialize their access to the static Console class.
Console.WriteLine("{0:####.####}", mc.GetValue(i))
pool.PutObject(mc)
If cts.Token.IsCancellationRequested Then
loopState.Stop()
End If
End Sub)
Console.WriteLine("Press the Enter key to exit.")
Console.ReadLine()
cts.Dispose()
End Sub
' A toy class that requires some resources to create.
' You can experiment here to measure the performance of the
' object pool vs. ordinary instantiation.
Class TestClass
Public Nums() As Integer
Public Function GetValue(ByVal i As Long) As Double
Return Math.Sqrt(Nums(i))
End Function
Public Sub New()
Nums = New Integer(10000000) {}
' ReDim Nums(1000000)
Dim rand As Random = New Random()
For i As Integer = 0 To Nums.Length - 1
Nums(i) = rand.Next()
Next
End Sub
End Class
End Module